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Looking Beyond Herbicides

WEED FRAGMENTS: Boat crews pull invasive weeds from the Tahoe Keys canals, which are fragments left over from the harvesters. New methods to pick up fragmens will be tested this summer. Photo courtesy of Freshtracks

INVADERS: Scientist Lars Anderson pulls a mass of Eurasian milfoil, a type of aquatic invasive species, from the Tahoe Keys lagoons in August 2015. Photo courtesy of Freshtracks

Battling aquatic invasive weeds is an ongoing issue for South Lake’s Tahoe Keys, which was told by the Lahontan Regional Water Quality Control Board in December that it had to evaluate non-chemical methods before considering the use of herbicides to combat the weeds. In response, the Keys will perform a number of field tests this summer evaluating various methods to control the invasive plants. Additionally, a permit application will be submitted to Lahontan this summer requesting to test aquatic herbicides in 2017.

“We want to come up with the best plan possible to implement it on a full scale,” said Rick Lind, president and owner of the Sierra Eco System Associates, which is managing the plan. “We don’t have all the answers yet.”

While the draft of the Tahoe Keys Integrated Weed Management Plan, which was released in August 2015, looked to address the aquatic invasive weed issue by using herbicides, Lahontan noted that it would not be able to accept the plan “since the current permit does not authorize herbicide use and requires use of non-chemical methods to be implemented and evaluated first.” The integrated weed management plan is required by the water board as part of a 2014 waste discharge permit that allows the Keys to operate its weed harvesters, use bottom barrier mats up to 5 acres at a time to control weeds, and operate its circulation system. Lahontan extended the Keys’ deadline for submittal of the final plan to May 31.

The Tahoe Keys Property Owners Association will conduct several studies this summer, including using UV lights on Eurasian milfoil, a tank study testing the effectiveness of herbicides in tanks, and a dye study in the main lagoon that looks at the waterflow around the entrance to the lagoons and water movement. The studies and additional research will cost the homeowners association $520,000, which has already invested more than $750,000 in addressing the weed problem.

“The heavy-handed approach of using herbicides seemed premature,” said Jesse Patterson, deputy director of the League to Save Lake Tahoe. “What they are proposing seems much more pragmatic. We support looking at any non-herbicide method as a trial at Lake Tahoe.”

Lind said a permit application will also be submitted to Lahontan this summer seeking to conduct a pilot test demonstration of aquatic herbicides on 10 to 20 acres in the Tahoe Keys May and June of 2017. Patterson said the League would have to evaluate the specific details of any proposed test demonstration of herbicides in Tahoe before supporting such a demonstration, but noted that it “makes a lot more sense than a full-fledged assault.”

The 760-acre development, which includes 11 miles of lagoons and channels, will also continue management of invasive Eurasian watermilfoil and curlyleaf pondweed though scientists have said total eradication of the weeds in the Keys is not possible. New weed harvesting and fragment collection practices will be implemented this summer, including attaching nets to the five weed harvesters and setting up a boat backup station where skimming crews will be on hand to collect fragments. The homeowners association will also test three boats, which cost between $50,000 to $100,000, and are designed for fragment collection to see which type would be best for the Keys.

“We received comments that included creative and innovative thinking that has caused us to reevaluate and reconsider other control methods to come up with the best plan possible,” Lind said.

The Lake Tahoe Aquatic Invasive Species Coordination Committee also recently loaned 130 bottom barrier mats to Tahoe Keys residents, who volunteered to place the mats near their docks. The mats block sunlight and eventually kill the weeds. Bottom barriers were tested last summer by one property owner, and those participating this year will give feedback on the experience to inform future efforts.

“The whole Tahoe Keys community is very interested in eradicating these weeds,” Linda Callahan, manager of the Architectural Control Department for the association, stated in a release. “There’s a lot of enthusiasm to be part of the solution — people are eager to help.”

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